Hitherto, there are known plate making processes using lithographic printing machines, namely on-printing machine plate making processes. For example, in Japanese Patent Application Laid-Open (KOKAI) No. 11-216835(1999) as filed by the present applicant, there is described an improved on-printing machine plate making process. In this on-printing machine plate making process, a photosensitive lithographic printing plate is produced using a lithographic printing machine having a printing section including a plate cylinder, a blanket cylinder and an impression cylinder, by (A) supplying a plate-treating agent to a photosensitive lithographic printing plate fixed on the plate cylinder and exposed to image light, from a plate-treating agent feeding roller disposed in contact with the photosensitive lithographic printing plate; and then (B) rotating the plate cylinder and the blanket cylinder while keeping both the cylinders in contact with each other, so as to apply physical stimulus to the photosensitive lithographic printing plate, thereby forming images thereon.
The above process is characterized in that the step (B) is conducted after causing the blanket cylinder and the impression cylinder to be spaced apart from each other, and further stopping delivery of papers to the impression cylinder. In such a process, after the printing plate is produced by fixing the photosensitive lithographic printing plate exposed to image light, on the plate cylinder, printing procedure is successively conducted using the thus produced printing plate. This process is intended to reduce loss of papers and to prevent dirt or dusts from mixing in the plate-treating agent (printing ink, dampening water, etc.).
However, in Japanese Patent Application Laid-Open (KOKAI) No. 11-216835(1999), there is described only the developing method using dampening water on the printing machine. Also, Japanese Patent Application Laid-Open (KOKAI) No. 11-216835(1999) neither describes nor suggests at all the regeneration of the printing plate after printing.
In Japanese Patent No. 3122717 (equivalent to EP802457A1), there is described the process in which a hydrophilic emulsion capable of being converted into hydrophobic one upon irradiating light thereto, is used as a photosensitive composition, and the photosensitive composition is subjected to light exposure and image development on a printing machine by a melting method. However, the thus produced printing plate must be further improved in wear resistance upon printing. In Japanese Patent No. 3122717, there is described only the developing method using dampening water on a printing machine. Also, although it is described that the printing plate may be regenerated after printing, the Japanese Patent No. 3122717 does not describe at all a concrete method for regeneration of the printing plate.
In Japanese Patent Application Laid-Open (KOKAI) No. 9-99535(1997) (equivalent to U.S. Pat. No. 5,713,287), there is described the on-printing machine image forming method using as a photosensitive composition, a switching polymer whose hydrophilic property is changeable to a hydrophobic property by irradiating a laser thereto. However, the printing plate obtained by this method must be further improved in wear resistance upon printing. Also, in the above method, no development step is provided independent of the printing step. Further, in Japanese Patent Application Laid-Open (KOKAI) No. 8-52949(1997) (equivalent to U.S. Pat. No. 5,816,161 and EP 693371A1), there is described the method of repeatedly erasing and reproducing images on a printing plate within a printing machine without removal of a plate cylinder or the printing plate. However, Japanese Patent Application Laid-Open (KOKAI) No. 8-52949(1997) fails to specify the developing and printing methods at all.
An object of the present invention is to provide a regenerative plate making and printing process as well as a plate making and printing apparatus by further improving the conventional on-printing machine plate making methods, which are considerably improved in working efficiency, and are capable of suppressing the generation of the stains upon printing, thereby producing stable high-quality images.